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Mail can not be delivered

Hello there,

From time to time our client does not receive email from us.
We got an NDR with the following:
--------------
Your message did not reach some or all of the intended recipients.
The following recipient(s) cannot be reached:
....

The e-mail system was unable to deliver the message, but did not report a specific reason.  Check the address and try again.  If it still fails, contact your system administrator.

#2.0.0 smtp;221 Service closing transmission channel closing connection
------------------

I've checked http://mxtoolbox.com/blacklists.aspx it shows our SMTP's IP is not black listed.
We have Exchange 2003, the client's mx's port 25 respond with "220 SMTP Proxy Server Ready"

What is the most probable cause of the problem?

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zc2
Asked:
zc2
1 Solution
 
december41991Commented:
This could not be a problem with you server most of the time. Its  that the recipient email address is not correct or those domain could not be resolved because MX record does not exist.
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zc2Author Commented:
Thank you for the answer,

Email address IS correct. The recipients gets the email from us most of the time. But sometimes he does not and we got that NDR. The missed mx record is even less possible, because
basing on the "#2.0.0 smtp;221 Service closing transmission channel closing connection" string in the NDR I guess the connection to the recipient's mx was established, but then something went wrong.
Is there any kind of test I could apply to find out what is wrong?
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december41991Commented:
Is this happening to any domain only or randon to any domain.
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zc2Author Commented:
Apparently it happens only when mail is sent to that one recipient.
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cracksalsaCommented:
A helpful way to sometimes identify what is going on is to establish a connection from the command line. Identify the mx record of the mail server you are connecting to. open command prompt and telnet to the mx record on port 25. For example, if the mx record points mail.otherdomain.com then type at the cmd prompt:
telnet
open mail.otherdomain.com 25
helo yourdomainname.com
mail from: youremail@yourdomain.com
rcpt to: recipent@otherdomain.com
data
<type your data here.. ie: test msg>
end session by typing . on its own line.
Usually somewhere in there you will see it reject the connection but it will give you more data.
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zc2Author Commented:
No there is nothing unusual.

220 SMTP Proxy Server Ready
HELO mysite.com
250 +OK SMTP server Ready
MAIL FROM:<myaddress@mysite.com>
250 +OK Sender OK
RCPT TO:<Recepient@otherdomain.com>
250 +OK Recipient OK
DATA
354 Start mail input, end with '<CR><LF>.<CR><LF>'
Subject: test again please respond
To: <Recepient@otherdomain.com>
From: <myaddress@mysite.com>
 
test. 
 
.
250 +OK message queued for delivery.

Open in new window

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pressonjCommented:
Seems to me the issue is that your recipient is using an SMTP proxy server in front of the email server  (220 SMTP Proxy Server Ready)

Sometime proxy server may drop connection to the SMTP server due to time out etc.  
The SMTP message "#2.0.0 smtp;221 Service closing transmission channel closing connection" in the NDR is most likely from the SMTP proxy server that dropped the connection.





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zc2Author Commented:
Is there what we could do, preferable on our side? Like rise the mail's importance level or something?
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zc2Author Commented:
The expert did not suggest anything to improve the situation and did not answered on my latest commnet.
I assume the answer he gave in his guessing is correct but that won't allow me to solve the problem.
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